Test set for measuring the angle represented by synchro voltages



P 1952 J. H. GERTH I 2,609,435

TEST SET FOR MEASURING THE ANGLE REPRESENTED BY SYNCHRO VOLTAGES FiledAug. 2 1951 5 Sheets-Sheet 1 BRIDGE I 5 7 1 l /o, 9 I l NULL 1f lDETECTOR x i 1 1 T i 5 I 1 l 1 .1

8 Ex .6 6 EA v 6 4 fi+1m-(0-ao")] 0 I0 J0 40 0 I00 0 I20 I20 I30 I40 I50I70 I80 I80 I90 200 2/0 220 230 240 240 250 260 270 280 290 .300 3 003/0 320 330 340 350 360 0- DEGREES IN VE N TOR J. H. GERTH 81 AT TOR-NEV Sept. 2,1952 GERTH 2,609,435

TEST SET FOR MEASURING THE ANGLE REPRESENTED BY SYNCHRO VOLTAGES FiledAug. 2, 1951 5 Sheets-Sheet 5 even 6020 miaao 602401205 180360 A 7'TOR/V5 V Patented Sept. 2, 1952 TEST SET FOR MEASURING THE ANGLEREPRESENTED BY SYNCHRO VOLTAGES .l'ohn H. Gerth, Winston-Salem, "6.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York ApplicationAngust 2, 1951, Serial No. 240,015

4 Claims. (Cl. H T- 337) 1 This invention relates to a device for testinsynchronous control transformers.

The object of the invention is a portable test set to measure the angleof rotation of the rotor of a synchronous control transformer asrepresented by the voltagesat the terminals of the three windings of thetransformer.

A feature of the invention is a bridge circuit connected to theterminals of the three windin s of the transformer, including apotentiometer arrangement for indicatinga-ratio of the voltages at theterminals of the three windings of the transformer. The potentiometerarrangement may include a plurality of potentiometer resistors connectedin serial relationship and a plurality of equal shunt resistorsrespectively connectable in parallel relationship with saidpotentiometer resistors, said potentiometer resistors being soproportioned that, with said shunt resistors, the potentiometer ratio ofthe junction of each two potentiometer resistors corresponds to adifferent known angle of. rotation of the rotor.- I

Another feature of the invention is a linear potentiometer with awinding having the same resistance as the equal shunt resistors, andswitching means for substituting the linear potentiometer winding forone of the shunt resistors.

A furtherfeature of the invention is a resistor, having the sameresistance as the combined resistance of the potentiometer and shuntresistors, connected in serial relationship therewith, and switchingmeans for connecting this combination of resistors directly, orinvertedly, to the windings of the synchro transformer.

Another feature of the invention is switching means for connecting thethree terminals of the synchro transformer, in any desiredorder to thetesting circuit.

Their-mention will be better understood from the following description,when read in conjunction with the drawings, inwhich: I V

Fig. i isa simplified schematic showing of a synchro control transformerand test set;

Fig. 2 is a curve of the computed test values plotted againstthe-'synchro angle;

Fig. 3 is a simplified schematic of a typical test set embodying the'invention;

. Fig. 4 is a top view of the test set of 'Fig. 3; and Fig. 5 is a frontview of the test set of Fig. 4. Fig. 6 is a detail view of the movableshutter 80 shown in Fig. 5. V

A synchro control transformer has the form of a small electric motorhaving an exciting winding arranged to have rotarymotion with res ect tothree phase windings, The exciting winding may beon the rotor and thephase windings on the stator, or vice versa, so long as the windings maybe rotated with respect to each other. The exciting winding is commonlyarranged for connection to a single phase source, though a multiphasewindingmay beusecl; and the phase windings may be connected in Y ordelta. In some cases, the phase windings may be the exciting windings. pi

For convenience of description, and not as any limitation on the scopeof the invention, the synchro transformer I, shown in Fig. 1, has arotary single phase exciting winding 2, connected by terminais Ri, R2,to a suitable source3, and phase windings 4, 5, 6 connected in Y, andrespectively connected to terminals S5, S2, S3, which are respectivelyconnected to terminals A, B, C. To measure the angle of rotation of theexciting winding,- two equal resistors I, 8, are respectively connectedbetween terminals AB and AC; and a potentiometer winding 9, having aresistance equal to the resistance of resistor 1 is connected toterminals BC. A null detector is, or other suitable meter, is connectedfrom the junction of resistors l, 8, to a brush H contacting the winding9.

Let 0 be the angle of rotation of the exciting field measured clockwisefrom the position where equal voltages are induced in the windings 4 and6; EA be the voltage drop across'the winding 9; and Ex the voltage fromterminal C to brush I I, when brush I I is adjusted to; make the nulldetector lflread zero. Under these conditions, it may be shown that forvalues of 0'between 0: and degrees:

as given in Equation 1, is plotted in Fig. 2, against the angle 0. Asthis is a potentiometer ratio, the values of this ratio must be between0 and 1'. For values of 0 from 0, to 60 degrees, and alsofrom 180 to 240degrees, the values of the right side of Equation 1' also lie between 0and l, and a solution of Equation 1 is possible. For these values of 0between 0 to 60 degrees, and 180 to 240 degrees, the voltage S253 isofone polarity, and the voltages SISZ, and S3Sl' are of opposite polarity.Now,-for values of 0 between 60to degrees, and 240 to 300degrees, thevoltage S36! is of one polarity,and the'voltages SISZ and S283 are ofopposite-polarity, thus, owing to the symmetrical arrangement of thewindings, if the connections shown in Fig. 1 are changed to connect SIto C, S2 to A, and S3 to B, Equation 1 may be solved. Similarly. forvalues of between 120 to 180 degrees, and 300 to 360 degrees, thevoltage SIS2 is of one polarity, and the voltages S2S3 and S351 are ofopposite polarity, thus, if the connections shown in Fig. 1 are changedto connect SI to B, S2 to C, and S3 to A, Equation 1 may be solved.

In Fig. 3, the terminals SLSZ, S3, of the synchro transformer beingtested are respectively connected to terminals A, B, C.- With switch 32in the first position, moving switch 3i to the lowest position willconnect Sl to H, the junction of resistors I, 8, S2 to G, the terminalof resistor 1, S3 to I, the terminal of resistor 8, as shown in Fig. 1,for angles of 0 to 60 degrees, and from 180 to 240; moving switch 3| tothe second position will connect SI to 1, S2 to H, and S3 to G, as shownin Fig. 3, for values of 0 from 60 to 120 degrees, and from 240 to 300degrees; moving switch 3! to the highest position will connect SI to G,S2 to I, and S3 to H, for values of 0 from 120 to 180 degrees, and from300 to 360 degrees.

In-Fig. 2, a straight line has been drawn through the extreme values ofEquation 1. In some prior testing systems, a bridge circuit similar toFig. 1

was used; the potentiometer winding 9 varying linearly in resistance.For equal increments of movement of the brush, the potentiometer ratioswill fall on the straight line in Fig. 2, and, either a complicatedformula must be used to convert these potentiometer ratios into thecorresponding values of 0; or the potentiometer dial must be calibratedin unequal steps. Again, while the potentiometer wire could be wound onan insulating card soshapedthatth potentiometer ratios would have thevalues required for the solutionof Equation 1, for reasonable accuracy,'such a shaped potentiometer would be bulky, fragile, and expensive. 7

In accordance with the present invention, a plurality of resistorsconnected in serial relationship, or a single tapped resistor, areselected to give accurately the potentiometer ratios indicated by thedots in Fig. 2, and a linear, auxiliary potentiometer is combinedtherewith to give values intermediate of the values shown by dots.

In Fig. 2, the curve of Equation 1 is symmetrical about the mid-point,thus, in accordance with the present'invention, a fixed resistor, havingthe same resistance as the sum of the resistances of the potentiometerresistors, is connected in serial relationship therewith, and thepotentiometer resistors are selected to give the ratios indicated bypoints I to 6. The connections to the combination of resistors are theninterchanged, and the potentiometer resistors will then give the ratiosindicated by points"! to I12.

In Fig. 1, t have equal loading on the phase windings, the resistancesof 1, 8, 9, preferably are equal; and, to reduce the load on thesynchro, for normal conditions, these resistances may be, say, 10,000ohms. For other typesv of synchro, other suitable values. of these.resistances may, of course, be used. 3 V

In Fig. 3, terminal G of resistor 1 is connected by connection 49 toresistor 33, and terminal I of resistor 8 is connected by connection 56to resistors 39, 45. Resistor 33 is connected in serial relationshipwith the combination of resistors 34 to 39. For steps I to 6 of switch32, terminal D is connected to terminal I and terminal E is connected toterminal G, so that the potentiometer resistors may give ratiosindicated by points I to 6 of Fig. 2; for steps 1 to l2 of switch32,,terminal D is connected to terminal G and terminal E is connected toterminal I, thus reversing the connections to the bridge circuit so thatthe potentiometer resistors may give the ratios indicated by points I tol2 of Fig. 2.

The values of Equation 1 are, approximately v Degrees... 0 l0 Values 0097 .185 268 347 124 500 Degrees Values 576 653 732 815 903 l. 000

Assume resistor 33 is 5000 ohms, and that re sistors 34 to 39, withtheir associated shunt resistors respectively have resistances of 757,739, 793, 830, 883, 968 ohms. With the free end of resistor 39 as zero,the potentiometer ratios of the junctions of resistors 39m 34 willrespectively be .097, .185, .268, .347, .424, .500, in agreement withthe values of Equation 1 for 0 from 0 to 30 degrees. With theconnections reversed, and the free end of resistor 33 as zero, thepotentiometer ratios of the junctions of resistors 34 to 39 will be.576, .653, .732, .815, .903, 1.000, in agreement with the values ofEquation 1 for 0 from 30 to 60 degrees.

The resistors 1, 8, preferably have equal resistances, of, say 10,000ohms; the resistor 33 may have half this resistance, and the combinationof resistors 34 to 46- may have the same resistance as resistor 33. Theupper terminals of resistors 34to 39 are respectively connected to allbut two of the contacts of switch 48. The blades of switch 48 arerespectively connected to the free terminalsof resistors 40 to 45; theother terminals of these resistors being respectively connected to thelower terminals of resistors 34 to 39. The resistors 40 to 45, and thepotentiometer winding 46, have the same resistance, say 10,000 ohms; Theresistors 34 to 39 are selected so that, when connectedin parallel witha resistor of this value, the respective junctions of resistors 34 to 39will give the potentiometer ratios showninFig. 2.

,The junction of resistors 33, 34, is connected by conductor 50 to allcontacts but contacts 6, I, of the upper bank ofswitch 48, to contact 1of the upper bank ofswitch 4! and to contact 6 of the lower bank, of,switch 41 When switches 41, 48 are on the 6th contact, resistor 40 isdisconnected, connection 50 is connected through the 6th contact of thelower bank of switch 4] and the winding 46 to the 6th contact of theupper bank of switch 41*, and conductor 5|, thus substitutingthe-winding 46 for resistor 40. In the 7th position of switches 41, 48,resistor 40-is also disconnected, connections 50is connected through the7th contact of upper bank of switch 47, and the winding 46 to; the 7thcontact of the lower bank Of switch 41 and conductor 5!. Thus, in the6th and 7th positions'of switches 41, 48, the winding 46 is substitutedfor the resistor 40; and in the 7th position the connections of winding46 are reversed. Switches 32,41, 48, are preferably one 12-position,IO-bank switch, in which all the switchblades are moved simultaneously.Due to the reversal of connections to the bridge when switch 32 is movedfrom the 6th contact to the, 7th contact, 'the connections of winding 46are similarly reversed when passing from'a contact, less" than 1 to acontact greater than 6. .7 I

The second bank of switchtsubstitutes the winding 46 for resistor 4| onthe 5th and 8th contacts; the third bank of switch 48 substitutes thewinding 46 for resistor 42-011 the 4th and 9th contacts; the fourth bankof switch 48 substitutes the winding 48 for resistor 43 onthe 3rd and10th contacts;-the fifth bank of switch 48 substitutes the windingjliifor resistor 44 on the 2nd and 11th contacts; and the sixth bank ofswitch 48 substitutes the winding 46 for resistor 45 on the 1st and 12thcontacts.-

The first six steps of switches 41, 4t successively substitute thewinding 46 for resistors 45 to 40, whileswitch 32 maintains one setofconnec tions to resistors 1, 8; the second six steps of switches 41,48 successively subtitute the winding 46 for resistors 40 to 45, whileswitch 32 reverses the connections to, resistors 1, 8. The brushcontacting winding 45, is connected through the null detector-l3 "to thejunction H of resistors 1, 8. The successive junction points ofresistors 39 to 33, with the correspondingshunt resistors, givethecorrect potentiometer ratios for each five degrees, as shown on Fig. 2,and the potentiometer ll, 46, linearly interpolates bee tween thesevalues.

Figs. 4 and 5 show a convenient structure embodying the circuit of Fig.3, and having a mounting plate 6!; equipped with handles 62, 52, forconvenience in sliding the test set into an appropriate container (notshown) 'to'which the plate 6| may be secured, as by screws 83, 63. Asecond mounting plate 64 is supported by plate El, and spaced therefromby spacers 65, 65, secured by bolts 66, 66. The range selector switch 3|is mounted on plate 64 with the shaft extending through plate 6| to theoperating knob 68. The larger resistors 1, 8, 33, may conveniently bemounted on plate 64, and secured by a suitable clamp 61. The coarseangle switches 32, 41, 48, may be mounted on plate 64, with the shaftextending through plate 6| to the operating knob 69. Resistors 34 to 45may be mounted between the decks of switch 48, and, as this assembly ofswitches 32, 41, 48, and resistors 34 to 45 may be comparatively heavy,the assembly may be supported by a sheet metal support 1| secured in anysuitable manner to plate 64. Potentiometer 46 may be secured to plate 64with the shaft extending through plate 6| to the operating knob 10. Thecable from the synchro being tested is plugged into jack 12, while thenull detector is plugged into jack 13.

A small window 14 is cut through plate El, and covered by a transparentshield 55 to expose the dial 15, of potentiometer 46. The dial 16 mayconveniently be graduated from D to 5 degrees in 0.1-degree steps.

A second window 11 is cut through plate 6|, and covered by a transparentshield 13 to expose the dial 19 associated with switches 32, 41, 48. Inaccordance with Fig. 2, the dial i9 has six angles marked for each step,the two central angles being located on the radius of the dial, and theother four angles parallel thereto. The first step is graduated thesecond step and so on for the remaining ten steps.

A movable shutter 80 is secured to the shaft of switch 3| and interposedbetween the dial 19 and the window 11. As shown in Fig. 6, three slots8|, 82, 83 are cut in the shutterBfl in such locations that, when switch3| is. in the first position, slot 8| exposes only the lower one-thirdof window 11, and the markings on dial 19, 0, 5, etc. When switch 3| isin the second position, slot 82 exposes only the central onethird ofwindow 11, and the markings on dial 19, 60, 240; 65, 245; etc. Whenswitch 3| is in the thirdposition, slot 83 exposes only the upperone-third of window 11, and the markings on dial 19, 120, 300; 125, 305;etc. When the test set has been adjusted to null the detector, thesynchro' angle is the sum of the readings of dials 19, 16. Two readingswill be shown on dial 19, spaced apart by 180 degrees, but thisambiguity may easily be resolved by visual inspection of the synchrobeing tested.

If the synchro angle is unknown, the test may conveniently'be made asfollows: with switches 32, 41, 48, in any position, adjust switch 3|till the null detector it gives a minimum reading. The dial of switch 3|is graduated to indicate the (SO-degree range of the reading. Switches32, 41, 4 8 are then adjusted until the detector It reads a minimum. Thedials of these switches are graduated to indicate the 5-degree range ofthe reading. If the angle lies near one end of the 60- degree range, itmay be necessary to readjust switch 3| and switches 32, 41, 48. Thebrush H is then adjusted till the detector |0 shows an exact null. Thedial brush is graduated in degrees, and tenths of degrees. If the angleis some integral multiple of five degrees, it will not be possible tonull the detector H1 exactly. With switches 32, 41, 48 set at thecorrect angle, the detector I!) will approach a null as the brushapproaches zero, but will not pass through the null reading. Switches32, 41, 48, may then be set to the next lower range and brush 1 movedtoward the maximum. If the detector Hi again approaches a null, withoutpassing through the null reading, the angle is an integral multiple offive degrees. The synchro angle is the sum of the angles indicated bythe dials actuated by the shafts moving the switches 3|, 32, 41, 48, andbrush II.

It is to be understood that the above-described arrangements areillustrative of one application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. Apparatus for determining the angle of rotation of a synchrotransformer having an exciting winding capable of relative rotary motionwith respect to three phase windings respectively connected to phaseterminals comprising: two equal resistors connected in serialrelationship, a null detector connected to the junction of saidresistors. a potentiometer having resistor means equal in resistance tothe resistance of either of said resistors connectable in parallelrelationship with said resistors and a brush contacting said resistormeans and connected to said detector, and a three-pole, three-positionswitch, having blades respectively connected to the free ends and thejunction of said resistors, and contacts connected amasses- 7 to saidphase terminals so arranged that the operation of said switch willconnect each phase terminal in succession to the junction of saidresistors and the other two terminals to the free ends of saidresistors.

2. The combination in claim 1 in which said resistor means includes afixed resistor connected in serial relationship with a potentiometerwinding, and switching means for reversing the connections of saidresistor means to said equal resistors.

3. A test set for measuring the electrical angle between one winding ofa synchronous device excited by a single phase source and anotherwinding having three phase tappings respectively connected to phaseterminals, said windings being supported for relative rotary motion,comprising first and second equal resistors connected in serialrelationship, a first three-pole three-position switch having thecontacts of each position respectively connected to said terminals, oneblade of said switch being connected to'the junction of said resistors,a two-pole, multiposition switch having two blades respectivelyconnected to the other two blades of said first switch, and contactsconnected in multiple to form two equal groups per pole, the firstgroups of the two poles being respectively connected to the free ends ofsaid first and second resistors and the second groups of the two polesbeing respectively connected to the free ends of the second and thefirst resistor, whereby the three terminals of the phase windings may beconnected in all possible arrangements to said free ends and thejunction of said resistors, a third resistor, and a steppedpotentiometer connected in serial relationship across the free ends ofsaid first and second resistors, said stepped potentiometer comprisinga'plurality of resistors connected in serial relationship, each resistorbeing connectable in parallel relationship with a shunt resistor, saidpotentiometer resistors being so proportioned with said shunt resistorsthat the junction of each two potentiometer resistors has apotentiometer ratio corresponding to a different angle of said device, alinear potentiometer having a winding equal in resistance to each ofsaid shunt resistors and a brush, a null detector connected from saidbrush to the junction of said first and second resistors, and amultipole, multiposition switch having the same number of positions assaid two-pole, multiposition switch, connected to said shunt resistorsand the winding of said linear potentiometer, whereby the winding ofsaid linear potentiometer may be successively substituted for said shuntresistors and the brush of said linear potentiometer may be adjusted toselect potentiometer ratios intermediate the ratios represented by thejunctions of said potentiometer resistors. V

4. The combination in claim 3 with a dial rotated by said two-pole,multiposition switch and having three sets of graduations respectivelydiffering by 60 degrees, the graduations in each set diiiering by 180degrees, and a shutter actuated 1 by said three-position switch toexpose only one set of said graduations for each position of saidswitch.

JOHN H. GERTH.

No references cited.

